This invention relates to a digital time-division multiplex telecommunication system.
In German Offenlegungsschrift No. 23 24 854 a method for directional message transmission in a network with multiple branching has been disclosed in which messages are to be sent only in those time intervals in which simultaneously no other subscriber device is sending. The message flows are to be directed by virtue of the fact that during the establishment of a connection, when the coded call numbers of the calling subscriber which are sent out in both directions into the whole network containing bidirectional two-wire transmission lines pass through network nodes, a marker is added to each of these call numbers and from the totality of these markers a routing address is formed which allows the path travelled by the call number to be recognized clearly. One of these calls which are sent out distributed over the whole network, that is the one arriving at the receiving location of the subscriber called, then possesses the routing address which is "correct" for the desired connection and which makes it possible to return a directed call acknowledgment. The routing addresses, including a location marker for the location of the subscriber device between two nodes, are mutually communicated to the subscriber devices and must be sent in the time interval channels, together with the messages to be transmitted, during the whole period of a connection. In addition, the network nodes must be equipped with systems by means of which the paths of the routing addresses significant to these nodes can be detected and used to derive control signals which cause the respective message blocks to be transferred into the associated network branch.
Although a directional message transmission by means of the routing addresses and location markers added to the message blocks needs to take place only via those network branches which are absolutely required for the connection between two subscriber devices, this known method does not make it possible to utilize a time interval channel in these network branches for several simultaneous connections which do not overlap with respect to these connections and this time interval channel and thus to reduce the number of channels or to increase the number of subscriber stations connected. Any problems arising in this connection are eliminated with this routing address method by the fact that--as already mentioned above--messages can be sent only in those time intervals in which simultaneously no other subscriber unit is sending. Since furthermore the message blocks to be exchanged must here also include the routing addresses and location markers, the time interval channels are not particularly well utilized for useful information.
With respect to utilizing a channel for useful information, telecommunication systems working with time-position addressing are more advantageous. Such a message transmission system, providing multiple access by the connected subscribers, is disclosed, for example, in German Offenlegungsschrift No. 22 08 396. After the connection has been completely established, the time channel concerned can transmit only useful messages during message transmission, apart from a time position occupancy marker and a message marker, since the channel concerned is selected during establishment of the connection and fixed with respect to the start of the frame for this connection by its ordinal number. Thus the destination address does not need to be also transmitted during transmission of messages since it is contained as timing information in the position the channel has in time with respect to the start of the frame and cannot be mistaken. In this known message transmission system containing a transmission network consisting of a pure branching network without closed loops and in the individual branches of a two-wire line serving in each case for bidirectional transmission purposes, the totality of all messages sent is carried in the whole network. Considering a condition in which a connection is not just being established, of all existing connections only those time slots are occupied which can be nested in the nodes without temporary storage. In such a system with nondirectional message transmission, the traffic occurring in the existing connections loads the whole network of conductors even if messages are exchanged by closely adjoining subscribers.